It is known that conventional soles typically have a structure in the following designs:    A)    a two-layer structure based on an outsole and an insole. (Leather, rubber, other materials)    B)    a multilayer structure comprising an outsole, midsole(s) and an insole, in which different materials such as leather, reclaimed leather, synthetic fiber fabrics, thermoplastics, especially impregnated board, EVA, rubber are used and are adhesively bonded or pressed together.
The bending stiffness of the sole in these embodiments can only be changed in the longitudinal direction by use of different materials or material combinations (harder, softer), but this does not allow any influencing of the vertical/diagonal flexibility which is decisive for the natural rolling characteristics of the foot.
Conventional soles thus comprise multilayer leather sheet materials which are adhesively bonded in a sandwich, i.e. the bending stiffness of the sole can admittedly be made softer or harder in the longitudinal direction of the different layers, but the vertical bending stiffness of such shoe soles cannot be influenced.